Activation of persulfate (PS) by ultraviolet light or transition metal catalysts has been extensively studied. However, little is known about the activation of PS by iron oxychloride (FeOCl) in the presence of visible light irradiation. Herein, the catalytic activity of FeOCl was developed for oxidative degradation of rhodamine B (RhB) with the FeOCl/PS/Vis process. The characterization of FeOCl for reaction kinetics, degradation mechanism, and catalyst stability was investigated. It is found that the redox cycle of iron species and photoinduced electrons formed on the FeOCl catalyst surface can effectively activate PS, to generate radicals. Based on quenching experiments and electron paramagnetic resonance, the photogenerated holes (h+) and sulfate radicals (SO4−•) are the predominant reactive oxidants for RhB decolorization, while superoxide radicals (•O2−) and hydroxyl radicals (•OH) are also involved. Moreover, FeOCl shows good catalytic performance in a wide range of pH values (pH = 3–10) and excellent reusability and stability, as well.